The development of a point of care device for measuring blood ammonia

Ammonia is produced in the body during the metabolism of amino acids. In the liver, it is converted to urea via the urea cycle and excreted by the kidneys as urine. Normal levels are between 11 to 50 µM, whereas a blood ammonia level of approximately 100 µM indicates pathology. Elevated blood ammonia is associated with a number of pathological conditions including liver and kidney dysfunction. Conditions such as these can affect brain function and can be fatal. Current blood ammonia analysis requires a laboratory blood test. Few, if any of the techniques used are suitable for point of care (POC) testing. The development of a reliable and simple method for blood ammonia determination is essential for clinical diagnosis and management of patient progress in order to prevent further debilitating illnesses developing, and extending life. This is particularly critical in many disorders such as hyperammonaemia of the newborn, inborn errors of metabolism including urea cycle defects, organic acidaemias, hyperinsulinism/hyperammonaemia, liver disease and other cause of hyperammonaemic encephalopathy. This thesis investigates the development of an electrochemical sensor for the measurement of ammonia in blood. Polyaniline has a known affinity for ammonia which operates on the deprotonation of the polyaniline backbone forming an ammonium ion. In this work, polyaniline nanoparticles were fabricated and inkjet-printed onto silver screen printed electrodes. The sensors were then incorporated into devices containing a gas-permeable membrane, which facilitated the measurement of gaseous ammonia from a liquid sample (blood) using electrochemical impedance spectroscopy. The combination of impedance spectroscopy with a gas-permeable membrane allowed the measurement of gaseous ammonia from solution. The ammonia device developed possessed refinements to enhance its sensitivity and included careful optimisation of other aspects of the measurement. For example, an air purge through the device gas chamber was employed to remove matrix interferences from the sensor and improve the specificity to ammonia. The pH of the sample to be analysed was modified in order to increase the mass of ammonia in solution, thus lowering the limit of detection (LOD) of the device. Finally, assay timings were optimised in order to increase the impedimetric response of ammonia. These optimisations resulted in the effective detection of ammonia in a liquid sample down to the lowest clinically relevant levels found in blood. The devices displayed an impedimetric baseline intra- and inter-variability of 25 and 6.9%, respectively for n = 15 over a period of 160 s. A calculated limit of LOD of 12 µM was achieved for human serum measurements. A coefficient of determination of 0.9984, slope of 0.0046 and an intercept of 1.1534 was obtained in human serum across the linear range of 25 to 200 μM ammonia (n = 3). The device was validated against a commercial spectrophotometric assay which resulted in excellent correlation (0.9699, p < 0.0001) with a slope of 1.4472 and an intercept of 0.5631 between both methods (n = 3). The devices could be stored in desiccant for up to five months and displayed minimal variation (0.64%) over time (n = 12)

Wearable chemo/bio-sensors for sweat sensing in sports applications: combining micro-fluidics and novel materials

In the last decade, we have witnessed an exponential growth in the area of clinical diagnostic but surprisingly little has been done on the development of wearable chemo/bio-sensors in the field of sports science. In particular, the use of wearable wireless sensors capable of analysing sweat during physical exercise can provide access to new information sources that can be used to optimise and manage athletes’ performance. Lab-on-a-Chip technology provides a fascinating opportunity for the development of such wearable sensors. In this thesis two different colorimetric wearable microfluidic devices for real- time pH sensing were developed and used during athlete training activity. In one case a textile-based microfluidic platform employing cotton capillarity to drive sweat toward the pH sensitive area is presented that avoids the use of bulky fluid handling apparatus, i.e. pumps. The second case presents a wearable micro-fluidic device based on the use of pH responsive ionogels to obtain real-time sweat pH measurements through photo analysis of their colour variation. The thesis also presents the first example of sweat lactate sensing using an organic electrochemical transistor incorporating an ionogel as solid-state electrolyte. In this chapter, optimization of the lactate oxidase stability when dissolved in number of hydrated ionic liquids is investigated. Finally, a new fabrication protocol for paper-based microfluidic technology is presented, which may have important implications for future applications such as low-cost diagnostics and chemical sensing technologies

Development, Optimisation and Applications of Screen-Printed Electrochemical Sensors

The sustainability of healthcare delivery depends on the adoption of new low-cost devices to support the transition of services from centralised generic models to home and community-based care models, through which the patient status can be monitored remotely. Easily accessible body fluids (like saliva, sweat and interstitial fluids) represent alternative sampling media to blood that in principle can be conveniently analysed through wearable sensors. For instance, continuous monitoring of pH in saliva would allow a better clinical management of pathologies that alter acid contents within the mouth. Similarly, the real-time tracking of sodium levels in sweat and other body fluids can assist clinicians in the diagnosis and treatment of Cystic Fibrosis. Furthermore, athletes could reap many benefits from an optimal strategy for personalised rehydration, which might be informed by continuously measuring the amount of minerals lost in sweat. Electrochemical sensors based on the combination of screen-printed working and solid-contact reference electrodes are versatile and low-cost tools that are effective in facing many of the challenges in current sensing technology. They can be readily adapted for the detection of several ionic species, and in this thesis, as an example, two electrochemical platforms to monitor pH in saliva and sodium in sweat are going to be presented. The final devices are minimally-invasive and wearable, with a compact format due to the integration of miniaturised solid state ion-selective and reference electrodes. The technological advancements developed for their realisation are significant contributions for the more flexible design of novel miniaturised sensors for remote monitoring in general. Future developments of this technology could be pivotal for realising devices for applications as diverse as sensors integrated into fabrics for personal health monitoring, or autonomous sensors deployed in rivers and lakes for monitoring water quality

Development of medical point-of-care applications for renal medicine and tuberculosis based on electronic nose technology

Introduction: Current clinical diagnostics are based on biochemical, immunological or microbiological methods. However, these methods are operator dependent, time consuming, expensive and require special skills, and are therefore not suitable for point-of-care testing. Recent developments in gas-sensing technology and pattern recognition methods make electronic nose technology an interesting alternative for medical point-of-care devices. Methods: We applied a gas sensor array based on 14 conducting polymers to monitor haemodialysis in vitro and to detect pulmonary tuberculosis in both culture and sputum. Results and discussion: The electronic nose is able to distinguish between control blood and “uraemic” blood. Furthermore, the gas sensor array is not only capable of discriminating pre- from post-dialysis blood (97% accuracy) but also can follow the volatile shift occurring during a single haemodialysis session. The electronic nose can be used for both dialysate side and blood-side monitoring of haemodialysis. The pattern observed for post- and pre-dialysis blood might reflect the health status of the patients and can therefore be related to the long-term outcome. Furthermore, the gas sensor array was also able to discriminate between Mycobacterium spp. and other lung pathogens such as Pseudomonas aeruginosa. More importantly the gas sensor array was capable of resolving different Mycobacterium spp. such as Mycobacterium tuberculosis, M. scrofulaceum, and M. avium in both liquid culture and spiked sputum samples. The detection limit for M. tuberculosis in both sputum and liquid culture is 1 x 104 mycobacteria ml-1 and therefore partially fulfils the requirement set by the WHO. The gas sensor array was able to detect culture proven TB with a sensitivity of 89% and a specificity of 91%. Conclusions: In conclusion, this study has shown the ability of an electronic nose as a point-of-care device in these areas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)

Development of a handheld breath analyser for the monitoring of energy expenditure

Metabolic rate is not routinely assessed in healthcare for the general population, nor is it a measure commonly recorded for in-patients (incorrect feeding can slow post-operation recovery rate). For the general community, this lack of knowledge prevents the accurate determination of calorific need and is a factor contributing towards the onset of an overweight and an increasingly obese population. In the UK alone, obesity costs the National Health Service a staggering £5 billion annually. In this thesis a novel low-cost hand-held breath analyser is presented in order to measure human energy expenditure (EE). A unique optical CO2 sensor was developed, capable of sampling exhaled breath with a fast response time ~1 s and resilience to a humidity range of ~30 % to near saturated. The device was tested in a laboratory gas testing rig and a detection limit of ~25 ppm CO2 was measured. A low power metal oxide sensor (~100 mW) was developed to detect volatile organic compounds (VOCs) in the breath, for disease detection and investigation of the variation of inter-individual metabolism processes. The device was sensitive to acetone (100 to 300 ppm, which is a biomarker for type-I diabetes). Other VOCs, such as NO2 were tested (10 to 250 ppb). Further work includes investigating the inter-individual variance of metabolism processes, for which the metal oxide sensor would be well-suited. Software was developed to operate the gas testing rig and acquire sensor output data in real-time. An application was written for smartphones to enable EE measurements with the breath analyser, outside of a laboratory environment. Three hand-held analysers were constructed and tested with a trial of 10 subjects. A counterpart (benchmark) unit with medical grade commercial sensors (cost of ~£2500) and hospital respiratory rooms (reference) were included in the trial. The newly developed analysers improved upon the performance of the benchmark system (average EE measurement error +2.4 % compared to +7.9 %). The affordable device offered far greater accuracy than the traditional method often used by practitioners (predictive equations, error +41.4%). It is proposed a set of periodic (hourly) breath measurements could be used to determine daily EE. The EE analyser and associated low-cost sensors developed in this work offer a potential solution to halt the growing cost of an obese population and provide point-of-care health management

Grape pomace application in environmental studies: from waste to natural food preservative and source of biofuel

The geographic location of Republic of Macedonia is exceptional for breeding vine and specific grape varieties. But, the wine industry waste in general is a problem in Macedonia, since it does not have any usage. In the European Union, there is approximately 14.5 million tons of wine industry waste produced from wineries (http://www.academicwino.com/2012/11/grape-seed-extract-leather-production.html). In fact, the wine industry waste (grape pomace) contains primarily crushed grape skins and seeds rich in beneficial polyphenol compounds that act as antioxidants, antibacterial agents etc. The largest fraction of winery waste is pomace, or the solid remains of grapes (skins, stalks and seeds), which is thrown away ending up in landfills. From another point of view, transport is the third largest emitter of greenhouse gases and biofuels can significantly reduce transport’s carbon footprint since it is dependent on finite fossil fuels such as oil and petroleum for its energy needs (R.E.H. Sims, et al.). Biodiesel, provides significantly reduced emissions of carbon monoxide; compared to petroleum diesel fuel